Thermal cracking process employing hydrogen donor



De@ 23 1,958 N. w. FRANKE ETAL v2,865,836

THERMAL CRACKING PROCESS EMPLOYING HYDROGEN DONOR Filed Nov. 10. 1952 hun,

'THERMAL CRACKING PROCESS EMPLOYING HYDRDGEN DONOR Norman W. Franke and Meredith M. Stewart, Penn Township, Allegheny County, Pa., assignors to Gulf Research & Development Company, Pa., a corporation of Delaware Application November l0, 1952, Serial No. 319,764 2 Claims. (Cl. 208-57) This invention relates to a cracking process and more particularly to the conversion of relatively high boiling United States Patent Qgi petroleum hydrocarbon fractions into valuable lower boiling hydrocarbon fractions.

In recent years great advances have been made in the cracking of intermediate boiling range petroleum hydrocarbon fractions to valuable lower boiling products such as gasoline. For example, various catalytic cracking processes, such as fixed-bed cracking processes like the Houdry process, moving-bed catalytic cracking processes such as the Thermofor Catalytic Cracking process and the Houdriow process, and the lluid catalytic cracking process have gained wide spread adoption in the petroleum relining art.

The processes mentioned above are directed to the;

catalytic cracking of an intermediate boiling range petr'- leum hydrocarbon fraction, such as gas oil, by contacting the fraction with a suitable cracking catalyst, for example, a synthetic silica-alumina cracking catalyst, an activated montmorillonite cracking catalyst, or an activated halloysite cracking catalyst, at au elevated temperature ordinarily in the range of 750 to l100 F. to produce high yields of gasoline. During the course of the processes, carbonaceous contaminants are deposited upon the catalyst, after which the catalyst is regenerated by removing the carbonaceous contaminants by combustion at a temperature of the order of 1000 to 1200" F. In a fixed-bed catalytic cracking process, the regeneration is conventionally accomplished in situ in the reactor while in moving bed and lluid catalytic cracking processes the regeneration is effected in a regenerator separate from the reactor. v

The catalytic cracking processes produce, along with the desired low-boiling hydrocarbon fractions such as gasoline, a significant percentage of so-called catalytic cycle oil. This catalytic cycle oil has approximately the same boiling range as the fraction charged to the catalytic cracking converter, but does not readily lend itself to catalytic cracking conversion. Ordinarily, the cata lytic cycle oil is recycled to the catalytic cracking converter; however, the yield of gasoline derived therefrom is relatively low.

While the aforementioned catalytic cracking processes have proved valuable for the treatment of intermediate boiling range hydrocarbon fractions, they are not suitable for the treatment of heavy very high boiling petroleum fractions. Such high boiling fractions are most often -derived from the vacuum distillation of total or topped crudes and contain a high percentage of the semi-solid residuals present in petroleum crudes. When the very hig'h boiling fractions are cracked catalytically, they deposit large amounts of coke on the catalysts and quickly destroy the activity of the catalysts. Similarly, thermal cracking of the very high boiling fractions results in the y 2,865,836 4Patented nee. 2s, .195s

formation of large amounts of coke which tend in plug the apparatus and seriously shorten the onstream period of the thema] cracking unit. Largely because of the diflculties encountered in cracking the very high boiling fractions to more volatile fractions, heavy, high boiling fractions are produced in quantities making their profitable disposal a ditlicult problem to the reliner.

Our invention provides a process wherein catalytic cycle oil and high boiling petroleum fractions are couverted to valuable lower boiling products such as gasoline, with a minimum amount of carbonaceous contaminant formation. High boiling fractions which may be successfully treated by this invention to form gasoline and other more volatile fractions are very heavy and refractory crudes such as Baxterville crudes, vreduced crudes from which heavy cuts of more volatile components have been taken, such as vacuum still bottoms, and equivalent products. In general these fractions, hereinafter designated as liquid residues, will have boiling points above 950 F. and carbon residues above 5% and are refractory stocks which must b e cracked under very severe conditions. In "the case of vacuum still bottoms, this invention allows the successful thermal cracking of reduced crudes which have'been subjected to deeper vacuum topping than has been employed in conventional processing. In this invention, the liquid residues are mixed with hydrogenated catalytic cycle oil and thermally cracked at severe conditions with greatly reduced coke formation.

The hydrogenated catalytic cycle'oil is prepared by catalytically cracking a gas oil to produce catalytically cracked products comprising gasoline, light oil, and catalytic cycle oil. The gasoline and light oil are removed from the catalytically cracked products, and the catalytic cycle oil is then hydrogenated at a temperature of 650 to 750 F. and a pressure in excess of 250 pounds per square inch, preferably at a pressure of 500 to 2500 pounds per square inch. The hydrogenated catalytic cycle oil is then combined with the liquid residue in a ratio of at least one part by vweight of hydrogenated catalytic cycle oil to four parts by weight of liquid residue, and the mixture is thermally cracked at a tcmperature in the range of 800 to 1,000 F. and a pressure of about 400 to 1000 pounds per square inch to form valuable low boiling hydrocarbon products. At lower temperatures within this range longer cracking periods will be required. Preferably, the hydrogenated catalytic cycle oil should be mixed with the liquid residue inthe ratio of one part by weight of hydrogenated catalytic cycle oil to one or two parts by weight of liquid residue. Preferred conditions for thermally cracking the mixture of hydrogenated catalytic cycle oil and liquid residue are a temperature of 850 to 950 F., most preferably 900 to 950 F., and a pressure of 600 to 800 pounds per square inch. f

The single ligure of the drawings is a liow sheet illustrating the process of this invention in a diagrammatic manner.

Referring to the accompanying figure', a petroleum crude, such as a West Texas crude, enters the system through a line 10 and is passed to an atmospheric still 12. Atmospheric still 12 separates th straight run gasoline and light oil as overhead, and these are removed from the system by means of a line 14. The heavier com 'mospheric still 12 are subjected to vacuum distillation.

The overhead from the vacuum distillation comprising catalytic charge stock is withdrawn through-a line and passed to the base of a catalytic reactor 22, which in the form of the invention illustrated in the drawings is a uid type reactor.

The catalytic charge stock passes upwardly through liuid catalytic reactor 22 which contains a bed of dense phase fiuidized cracking catalyst particles maintained at a cracking temperature, for example, a temperature in the range of 750 to 1100 F. The cracked products obtained from the catalytic cracking of the catalytic charge stock are withdrawn from the fluid catalytic cracking reactor 22 through a cyclone separator 24, which returns entrained cracking catalyst particles to the dense phase of the uidized bed of cracking catalyst particles, and

the cracked products are then withdrawn through a line 26 to an atmospheric still 28. Catalyst is continually introduced into the reactor 22 through a line 30 and withdrawn through a' line 32 to a regenerator (not shown).

Atmospheric still 28 is operated to withdraw as overhead all material boiling below about 600" F., comprising gaseous hydrocarbons, cracked gasoline, and light oil, through line 34. The bottoms from the fractionation of the products from the catalytic cracking is a catalytic cycle oil preferably having a boiling range of 600 to 750 F. If desired, a portion of this catalytic cycle oil can be recycled to the liuid catalytic cracking reactor 22 (by any conventional recycling means, not shown). The advisability of recycling depends upon the relative amount of catalytic cycle oil and liquid residues obtained at the refinery, which varies among refineries and is a function of the nature of the crudes that are beingcharged and the various refining operations used in the given refinery. As set forth below, it is essential for the purposes of our invention that a ratio be maintained of at least one part by weight of material derived from the nondestructive hydrogenation of the catalytic cycle oil (hereinafter described) to each four parts by weight of heavy vacuum still bottoms, and preferably the ratio between these components should be 1:1 or 1:2. Accordingly, the amount of recycled catalytic cycle oil from atmospheric still 28 is regulated to conform with this requirement.

The catalytic cycle oil used in the process of our invention is withdrawn as bottoms from atmospheric still 28 through a line 36, mixed with hydrogen supplied through a line 38 and passed to hydrogenator 40, wherein it undergoes a non-destructive hydrogenation. The catalytic cycle oil, being a distillate product, should contain no residual material that will form carbon on the hydrogenation catalyst. Carbon formed in the catalytic cracking operation is deposited on the catalyst and is removed by the regeneration of the catalyst. The catalytic cycle oil may be a much wider cut than the preferred range listed above, and have a boiling point in the range of 400 to 950 F. The lower boiling components tend to dull the eifect of the hydrogenated cycle oil in the subsequent thermal cracking of the mixture of hydrogenated catalytic cycle oil and liquid residues, and, for this reason, a catalytic cycle oil boiling above 450 F. is desirable.

The hydrogenation is most advantageously accomplished in the presence of a catalyst such as the conventional sulfur-resistant hydrogenation catalysts of which tungsten sulfide, molybdenum suliide, nickel tungstate, etc. are the more common. The catalyst can be supported on either an active or an inert carrier; or can be utilized without a carrier. A commonly used catalyst is molybdenum oxide supported on alumina. Inasmuch as it is essential that substantial destructive hydrogenation be avoided, the temperature within hydrogenator 40 should be maintained in the range of 650 to 750 F. and the pressure should be in excess of 250 pounds per square inch, and preferably in the range of 500 to 2500 pounds per square inch. Hydrogen is with the drogenation should be conducted in a substantially nonregenerative manner permitting very long on-stream cycles without the deposition of excessive coke on the .hydrogenation catalyst. Typical flow rates range from to 2 volumes of cycle oil per volume of catalyst per hour. It will be appreciated that the conditions of time, temperature and pressure are interdependent and, additionally, will depend upon the particular catalytic cycle oil. The several variables of reaction conditions should be regulated to avoid destructive hydrogenation and to hydrogenate a major portion of the aromatic constituents of the catalytic cycle oil to hydro-aromatic components.

Hydrogenated catalytic cycle oil is withdrawn from the bottom of hydrogenator 40 through a line 42 and passed to a separator 44. Hydrogen is taken off overhead from the separator 44 through a line 46 and the hydrogenated cycle oil is withdrawn from the bottom of the separator through a line 48 and mixed with the liquid residue taken from the bottom of vacuum still 18 through line 50.

The mixture of liquid residue and hydrogenated catalytic cycle oil is introduced through a line S0 into a thermal cracking unit 52 wherein the mixture is thermally cracked at a temperature of 800 to 1000 F. and a pressure of 400 to 1000 pounds per square inch. The preferred ranges of operation in the thermal cracking unit 52 are at a temperature of 850 to 950 F. and a pressure of 600 to 800 pounds per square inch. Thermally cracked products are withdrawn from the termal cracking unit 52 through line 54 into a separator 56 in which gas from the cracking operation is separated from the high boiling liquid fractions and withdrawn overhead through line 58. The liquid fractions are taken from the bottom of separator S6 through a line 60 and passed to any suitable fractionating equipment, illustrated as an atmospheric still 62, wherein the cracked products are separated into a gasoline stream withdrawn overhead through line 64; a light gas oil stream taken from the still as a side stream through line 66; a heavy gas oil stream taken as a side stream through line 68; and residual oil which is withdrawn as bottoms through line 70.

The following examples illustrate the advantages secured in the process of our invention.

Example 1 One part by weight of Baxterville, Mississippi, crude, a very heavyl crude having heavy tar and coke forming properties and notably diicult to crack by conventional methods, having the following inspection:

was mixed with one part by weight of a fluid catalytically cracked West Texas catalytic cycle oil that had been hydrogenated in the presence of a molybdenum on alumina hydrogenation catalyst at a temperature of 710 F. and a pressure of 2500 pounds per square inch to produce a hydrogenated catalytic cycle oil having the following inspection: f

The mixture was thermally cracked in a bomb at a temperature of 824 F. for a period of 45 minutes. The initial pressure in the bomb was about 400 pounds per square inch gauge,l and the\linal pressure in the bomb was about 1000 pounds per square inch gauge. This cracking run Aproduced a product having the following inspection:

Weight percent of charge (No loss basis) Gas 5.8 Distillation:

Gasoline (below 392 F. B. Pt.) 44.3 Distilled products (above 392 F. B. Pt.)-- 11.6 Residue 35.5 Coke 2.8

Example 2 A run was conducted similarly to Example l save that the fluid catalytically cracked West Texas catalytic cycle I oil added to the Baxterville crude was not hydrogenate/j. The inspection of the fluid catalytically cracked West Texas catalytic cycle oil was as follows:

Gravity, A. P. I., 60 F C19.5 Distillation:

Initial boiling point, F 600 Volume percent (condensed)- 2 608 5 633 \10 651 20 l665 30 670 40 677 684 60 690 70 698 80 710 90 732 Aniline point, C 66.2 Bromine No 19.5 Olefns, volume percent 37.8 Viscosity, 100 F., centistokes 13.92

The products obtained from this thermal cracking run were as follows:

Weight-percent of charge (No loss basis) Gas 6.7 Distillation:

Gasoline (below 392 F. B. Pt.) 44.3

Distilled products (above 392 F. B. Pt.)-- 14.1

Residue 15.6

Coke 19.3

It should be noted that there is an increase in the yield of coke of the order of 600 percent in the second run, and a significant increase in the yield of gas, with out any corresponding increase in the yield of gasoline.

Further experiments were also conducted to determine whether a straight run distillate of the same boiling range as the catalytic cycle oil derived from the same vcrude used to obtain the catalytic cycle oil would have a similar inhibiting action on coke formation.

Example 3 A straight run West Texas distillate. having the following inspection: Gravity, AMPI Distillation:

Initial boiling point, F 420 2 438 5 450 10 456 20 473 30 486 40 500 50 515 533 553 574 600 614 End point, "F 631 Aniline point, F 67.0 Bromine No 4.6 Olelins, volume percent 6.2 Viscosity, F., centistokes 3.27'

was substituted for the hydrogenated catalytic cycle oil and another similar bomb run was conducted. The initial and final pressures at temperature were somewhat higher than in the above runs, being approximately 600 pounds per square inch gauge and 1380 pounds per square inch gauge respectively. This run produced a product having the following inspection:

Weight percent of charge (No loss basis) Gas 14.4 Distillation:

Distilled products 57.0

Residue 13.2

Coke 15.4

It is seen that again the yield of coke was many times greater than that obtained in the run conducted in accordance with the process of our invention, being of the orderA of 400 percent greater.

Example 4? A similar bomb run was also conducted utilizing a hydrogenated distillate derived by hydrogenating the straight 70 run distillate utilized in the previous bomb run at a temperature of 725 F. and a pressure of 2500 pounds per square inch in the presence of a molybednum oxide on alumina hydrogenation catalyst. In this run the initial pressure at temperature was 410 pounds per square inch 75 gauge and the inal pressure at temperature was 900 pounds per square inch gauge. The inspection of the product of `this run was as follows:

Again it is seen that the yield of coke is several hundred percent in excess of that obtained in the run conducted in accordance with the process of our invention.

While the foregoing description of our process constitutes a preferred operating procedure, it is obvious that our process may be modified by one skilled in the art. It is to be understood that these modifications constitute part of our invention and are to be considered as included within the appended claims. By way ofexample, in the accompanying ligure, the regenerator for the catalyst inventory of the uid catalytic cracking reactor, the preheaters, the valving means, pumps, etc., are omitted to clarify the description of the present invention. It is to he understood that the foregoing are to be construed as included therein inasmuch as their omission was effected solely to simplify the ligure. Moreover, while the embodiment set forth in the ligure shows the catalytic cycle oil derived from a tiuid catalytic cracking process, it is to be understood that catalytic cycle oils derived from other catalytic cracking processes can be utilized in the process of our invention. Furthermore, as heretofore indicated, only a portion of the catalytic cycle oil need be hydrogenated, and subsequently combined with the heavy liquid residues. Moreover, if desired, only a portion of the hydrogenated catalytic cycle oil from the hydrogenator need be mixed with the liquid residues, the remainder can be returned to the catalytic cracking reactor. lf the latter procedure is followed, it is preferable to return the lighter portion of the nondestructively hydrogenated catalytic cycle oil to the catalytic cracking reactor. Thus, an atmospheric still could be inserted after the hydrogenator, and the portion of the overhead from this atmospheric still comprising material boiling between 450 and 650 Cil F. d be returned to the catalytic cracking reactor. Th bottoms from this atmospheric still could then be combined with the liquid residue and thermally cracked in the thermal cracking unit.

The'process of our invention permits the thermal cracking of heavy liquid residue without the formation of the copious quantities of coke normally attendant to the cracking of these bottoms. Moreover, it also furnishes a means for converting catalytic cycle oil into relatively large quantities of valuable low boiling products.

Obviously many modifications and variations of the invention, as hereinbefore set forth, may be made without departing from the spirit or scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

We claim:

l. A process for thermally cracking virgin petroleum residues having boiling points above 950 F. and carbon residues above 5% comprising non-destructively catalytically hydrogenating a catalytic cycle oil at a temperature of 650 to 750 F., a pressure of 50o to 2500 ps. i., a hydrogen to oil ratio of 1000 to 10,000 cubic feet per barrel,and a space velocity of 56 to 2 volumes of cycle oil per volume of catalyst per hour, said catalytic cycle oil boiling above 600 F., mixing the hydrogenated catalytic cycle oil with the virgin residue in a ratio of at least one part of hydrogenated cycle oil four parts of virgin residue, and severely thermally cracking the mixture consisting of hydrogenated cycle oil and virgin residue at a temperature of 850 to 950 F. land a pressure in the range of 400 to 1000 p. s. i.

2. A thermal cracking process as set forth in claim 1 in which the yield of 392 F. end point gasoline produced in the thermal cracking step is at least about 40%, by

v weight, of the petroleum residue charge to the thermal cracking step.

References Cited in the ileof this patent UNITED STATES PATENTS 2,312,445 Ruthrul'f Mar. 2, 1943 2,426,929 Greensfelder Sept. 2, 1947 2,467,920 Voge et al Apr. 19, 1,949 2,502,958 Johnson Apr. 4, 1950 2,516,134 Molque- July 25, 1950 2,559,285 Douce July 3, 1951 2,678,263 Glazier.- May 11. 1954 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2,865,836 December 23, 1958 Norman W., Franke et al It is herebijr certified that error appears in the\printed specification of the above v"numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2, line l, for "tend in" read tend to column 8, line 2'7, after "oil" insert per l signed and Seal-ed this '7th day of Apri-1 1959.

(SEAL) Attest:

KARL H. AXLINE ROBERT C. WATSON Attesting Officer Commissioner of Patents 

1. A PROCESS FOR THERMALLY CRACKING VIRGIN PETROLEUM RESIDUES HAVING BOILING POINTS ABOVE 950*F AND CARBON RESIDUES ABOVE 5% COMPRISING NON-DESTRUCTIVELY CATALYTICALLY HYDROGENATING A CATALYTIC CYCLE OIL AT A TEMPERATURE OF 650*TO 750*F., A PRESSURE OF 500 TO 2500 P.S.I., A HYDROGEN TO OIL RATIO OF 1000 TO 10,000 CUBIC FEET PER BARREL, AND A SPACE VELOCITY OF 1/2 TO 2 VOLUMES OF CYCLE OIL PER VOLUME OF CATALYST PER HOUR, SAID CATALYST CYCLE OIL BOILING ABOVE 600*F., MIXING THE HYDROGENATING CATALYTIC CYCLE OIL WITH THE VIRGIN RESIDUE IN A RATIO OF AT LEAST ONE PART OFHYDROGENATED CYCLE OIL FOUR PARTS OF VIRGIN RESIDUE, AND SEVERELY THERMALLY CRACKING THE MIXTURE CONSISTING OF HYDROGENATED CYCLE OIL AND VIRGIN RESIDUE AT A TEMPERATURE OF 850* TO 950*F. AND A PRESSUE IN THE RANGE OF 400 TO 1000 P.S.I. 